In the field of the semiconductor technology, power devices are usually used as switches. Usually, it requires the power devices to endure a relative high turn-off voltage, and to have a relatively low on-state voltage. The commonly used power devices include Insulated-Gate Bipolar Transistors (IGBTs), or Vertical Double-diffused Metal-oxide Semiconductor (VDMOS) field effect transistors, etc.
FIG. 1 illustrates an existing IGBT. As shown in FIG. 1, the IGBT includes a substrate 1 doped with N-type ions; a gate 2 formed on the front surface S1 of the substrate 1; a P-type well region 3 formed in the substrate 1 and penetrating under the gate 2; and a source 4 doped with N-type ions formed in the P-type well region 3 at one side of the gate 2. The source 4 and the P-type well region 3 are electrically connected by the metal electrode 5; and the gate 2 and the metal electrode 5 are electrically insulated. Further, the IGBT also includes a buffer layer 6 doped with N-type ions formed on the back surface S2 of the substrate 1; and a collector layer 7 doped with P-type ions formed on the buffer layer 6. Along a direction perpendicular to the front surface S1, the P-type well region 3, the substrate 1, and the collector layer 7 form a PNP-type IGBT. The substrate 1 is the substrate of the PNP-type IGBT; and the P-type well region 3 is configured as the emitter of the PNP-type IGBT.
During the process for turning on and turning off the IGBT, a positive voltage is always applied on the collector layer 7. To turn on the IGBT, a turn-on voltage is applied between the gate 2 and the metal electrode 5 to form a channel on the surface of the P-type well region 3 under the gate 2. Thus, a base current is provided to the PNP-type IGBT; and the PNP-type IGBT is turned on. As shown in FIG. 1, the arrows illustrate the current direction. The doping concentration of the buffer layer 6 is higher than the doping concentration of the substrate 1. The N-type carriers in the buffer layer 6 diffuse into the substrate 1. Thus, the concentration of the carriers in the substrate 1 is increased; and the current is increased as well. Accordingly, the on-state voltage of the IGBT is reduced. To turn off the PNP-type IGBT, a turn-off voltage is applied between the gate 2 and the metal electrode 5. The channel disappears, and the PNP-type IGBT is turned off.
Because the positive voltage is always applied on the collector layer 7. Therefore, the PN junctions between the P-type well region 3 and the substrate 1 are reversely biased at off state. At the edge and corner of a power device, the breakdown voltage will be reduced because of the junction curvature.
To maintain the breakdown voltage of a power device, one approach is to form a termination structure around the power device. The termination structure may reduce the electric field peak at the corner and edge of a power device. Thus, the breakdown voltage of the power device is ensured. Further, after the subsequent wafer dicing process along the crube line in the substrate 1, the side surface of the substrate 1 may be uneven, the termination structure is able to prevent a current leakage issue caused by the depletion region end at the uneven side wall of the a power device die at off-state
A termination structures include field plates, field limit rings, or a combination thereof. The termination structures also includes deep-ring-trench termination structures, etc. The termination structure having a combination of field limit rings and field plate occupies a relatively large area of the power semiconductor device. Thus, the size of the power device having such a termination structure is relatively large.
Further, it needs extra processes to form the deep-ring-trench termination structure. The production cost is increased. The extra processes also affect the performance of cell structure of the power semiconductor device.
The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.